Method and apparatus for retransmission in communication system

ABSTRACT

An operation method of a first communication node in a communication system may comprise receiving one or more transport blocks (TBs) from a second communication node based on transmission parameters in an aggregated transmission period #n; generating decoding results for the one or more TBs; generating information required for changing the transmission parameters based on the decoding results; and transmitting the required information to the second communication node, wherein n is a natural number.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/086,724 filed on Nov. 2, 2020, which claims priority to Korean PatentApplications No. 10-2019-0141772 filed on Nov. 7, 2019, No.10-2019-0150338 filed on Nov. 21, 2019, and No. 10-2020-0128186 filed onOct. 5, 2020 with the Korean Intellectual Property Office (KIPO), theentire contents of which are hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to a retransmission technique in acommunication network, and more specifically, to a channel adaptationcontrol technique in a blind retransmission procedure.

2. Related Art

The communication network (e.g., a new radio (NR) communication network)using a higher frequency band (e.g., a frequency band of 6 GHz or above)than a frequency band (e.g., a frequency band of 6 GHz or below) of thelong term evolution (LTE) (or, LTE-A) is being considered for processingof soaring wireless data. The NR communication network may support notonly a frequency band of 6 GHz or below, but also a frequency band of 6GHz or above, and may support various communication services andscenarios compared to the LTE communication network. For example, usagescenarios of the NR communication network may include enhanced MobileBroadBand (eMBB), Ultra Reliable Low Latency Communication (URLLC), andMassive Machine Type Communication (mMTC).

The NR communication network may provide communication services toterminals located on the ground. Recently, the demand for communicationservices for planes, drones, satellites, etc. located not only on theground but also on the non-ground is increasing, and for this purpose,technologies for a non-terrestrial network (NTN) are being discussed.The non-terrestrial network may be implemented based on NR technologies.For example, in the non-terrestrial network, communications between asatellite and a communication node (e.g., user equipment (UE)) locatedon the ground or a communication node (e.g., airplane, drone) located onthe non-ground may be performed based on the NR technologies. In thenon-terrestrial network, a satellite may perform functions of a basestation in the NR communication network.

Meanwhile, in the communication network (e.g., LTE communicationnetwork, NR communication network, and non-terrestrial network), datamay be transmitted based on a blind retransmission scheme. In this case,a hybrid automatic repeat request (HARQ) response (e.g., acknowledgment(ACK) or negative ACK (HACK)) for the data may not be transmitted. Sincea transmitting node (e.g., base station or terminal) that hastransmitted the data may not receive the HARQ response for thecorresponding data, it may not accurately identify a state (e.g.,throughput) of a link. Therefore, resources may be wasted in the datatransmission procedure.

SUMMARY

Accordingly, exemplary embodiments of the present disclosure aredirected to providing methods and apparatuses for retransmission basedon statistical information with respect to data decoding results.

According to a first exemplary embodiment of the present disclosure, anoperation method of a first communication node in a communication systemmay comprise: receiving one or more transport blocks (TBs) from a secondcommunication node based on transmission parameters in an aggregatedtransmission period #n; generating decoding results for the one or moreTBs; generating information required for changing the transmissionparameters based on the decoding results; and transmitting the requiredinformation to the second communication node, wherein n is a naturalnumber.

The operation method may further comprise: receiving the transmissionparameters changed in consideration of the required information from thesecond communication node; and receiving one or more TBs from the secondcommunication node based on the changed transmission parameters in anaggregated transmission period #n+k, wherein k is a natural number.

The operation method may further comprise, when a number of the one ormore TBs is equal to a number of a plurality of slots included in theaggregated transmission period #n, transmitting a hybrid automaticrepeat request (HARQ) response for the one or more TBs to the secondcommunication node at a time indicated by the second communication node.

The required information may be transmitted to the second communicationnode when a feedback condition is satisfied.

The aggregated transmission period #n may include one or more slots, andthe one or more TBs received in the aggregated transmission period #nmay be generated based on a same data unit.

The required information may be statistical information indicating anumber of decoding successes or decoding failures occurring in theaggregated transmission period #n.

The required information may be statistical information indicating anumber of decoding successes or decoding failures occurring in one ormore aggregated transmission periods.

The required information may be information indicating that thetransmission parameters are not efficient.

The required information may be a guideline for changing thetransmission parameters.

According to a second exemplary embodiment of the present disclosure, anoperation method of a second communication node in a communicationsystem may comprise: transmitting transmission parameters to a firstcommunication node; transmitting one or more transport blocks (TBs) tothe first communication node based on the transmission parameters in anaggregated transmission period #n; receiving information required forchanging the transmission parameters from the first communication node;changing the transmission parameters in consideration of the requiredinformation; and transmitting the changed transmission parameters to thefirst communication node, wherein the required information is generatedbased on decoding results for the one or more TBs, and n is a naturalnumber.

The operation method may further comprise transmitting one or more TBsto the first communication node based on the changed transmissionparameters in an aggregated transmission period #n+k, wherein k is anatural number.

The required information may be received from the first communicationnode when a feedback condition is satisfied.

The aggregated transmission period #n may include one or more slots, andthe one or more TBs transmitted in the aggregated transmission period #nmay be generated based on a same data unit.

The required information may be statistical information indicating anumber of decoding successes or decoding failures occurring in one ormore aggregated transmission periods.

The required information may be information indicating that thetransmission parameters are not efficient or a guideline for changingthe transmission parameters.

According to a third exemplary embodiment of the present disclosure, anoperation method of a first communication node in a communication systemmay comprise: receiving a first transport block (TB) from a secondcommunication node based on transmission parameters; generating adecoding result for the first TB; generating information required forchanging the transmission parameters based on the decoding result;transmitting the required information to the second communication node;generating a hybrid automatic repeat request (HARQ) response for thefirst TB based on the decoding result; and transmitting the HARQresponse to the second communication node, wherein n is a naturalnumber.

The operation method may further comprise: receiving the transmissionparameters changed in consideration of the required information from thesecond communication node; and receiving a second TB from the secondcommunication node based on the changed transmission parameters, whereink is a natural number.

The required information may be transmitted to the second communicationnode when a feedback condition is satisfied.

The required information may be information indicating that thetransmission parameters are not efficient or a guideline for changingthe transmission parameters.

According to the present disclosure, a receiving node (e.g., basestation or terminal) may transmit statistical information on datadecoding results, efficiency information of transmission parameters,and/or guide information of transmission parameters to a transmittingnode (e.g., terminal or base station). The transmitting node mayreconfigure the transmission parameters based on the statisticalinformation, efficiency information, and/or guide information receivedfrom the receiving node. Communications between the transmitting nodeand the receiving node may be performed based on the reconfiguredtransmission parameters. Therefore, reliability in a retransmissionprocedure can be guaranteed, and resource waste can be prevented. Thatis, the performance of the communication system can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating a first exemplary embodimentof a non-terrestrial network.

FIG. 2 is a conceptual diagram illustrating a second exemplaryembodiment of a non-terrestrial network.

FIG. 3 is a block diagram illustrating a first exemplary embodiment ofan entity constituting a non-terrestrial network.

FIG. 4 is a conceptual diagram illustrating a first exemplary embodimentof a blind retransmission method in a communication system.

FIG. 5 is a sequence chart illustrating a first exemplary embodiment ofa retransmission method in a communication system.

FIG. 6 is a sequence chart illustrating a second exemplary embodiment ofa retransmission method in a communication system.

FIG. 7 is a conceptual diagram illustrating a first exemplary embodimentof a SAF required according to a result of decoding data in acommunication system.

FIG. 8 is a sequence chart illustrating a third exemplary embodiment ofa retransmission method in a communication system.

FIG. 9 is a sequence chart illustrating a fourth exemplary embodiment ofa retransmission method in a communication system.

FIG. 10 is a sequence chart showing a fifth exemplary embodiment of aretransmission method in a communication system.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure are disclosed herein. However,specific structural and functional details disclosed herein are merelyrepresentative for purposes of describing embodiments of the presentdisclosure. Thus, embodiments of the present disclosure may be embodiedin many alternate forms and should not be construed as limited toembodiments of the present disclosure set forth herein.

Accordingly, while the present disclosure is capable of variousmodifications and alternative forms, specific embodiments thereof areshown by way of example in the drawings and will herein be described indetail. It should be understood, however, that there is no intent tolimit the present disclosure to the particular forms disclosed, but onthe contrary, the present disclosure is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of thepresent disclosure. Like numbers refer to like elements throughout thedescription of the figures.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(i.e., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this present disclosure belongs.It will be further understood that terms, such as those defined incommonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand will not be interpreted in an idealized or overly formal senseunless expressly so defined herein.

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in greater detail with reference to the accompanying drawings.In order to facilitate general understanding in describing the presentdisclosure, the same components in the drawings are denoted with thesame reference signs, and repeated description thereof will be omitted.

A communication network to which exemplary embodiments according to thepresent disclosure are applied will be described. A communication systemmay be a non-terrestrial network (NTN), a 4G communication network(e.g., long-term evolution (LTE) communication network), a 5Gcommunication network (e.g., new radio (NR) communication network), orthe like. The 4G communication network and 5G communication network maybe classified as terrestrial networks.

The non-terrestrial network may operate based on LTE technology and/orNR technology. The non-terrestrial network may support communications ina frequency band of 6 GHz or above as well as a frequency band of 6 GHzor below. The 4G communication network may support communications in afrequency band of 6 GHz or below. The 5G communication network maysupport communications in a frequency band of 6 GHz or above as well asa frequency band of 6 GHz or below. The communication network to whichthe exemplary embodiments according to the present disclosure areapplied is not limited to the contents described below, and theexemplary embodiments according to the present disclosure may be appliedto various communication networks. Here, the communication network mayhave the same meaning as a communication system.

FIG. 1 is a conceptual diagram illustrating a first exemplary embodimentof a non-terrestrial network.

As shown in FIG. 1 , a non-terrestrial network may include a satellite110, a communication node 120, a gateway 130, a data network 140, andthe like. The non-terrestrial network shown in FIG. 1 may be anon-terrestrial network based on a transparent payload. The satellite110 may be a low earth orbit (LEO) satellite, a medium earth orbit (MEO)satellite, a geostationary earth orbit (GEO) satellite, a highelliptical orbit (HEO) satellite, or an unmanned aircraft system (UAS)platform. The UAS platform may include a high altitude platform station(HAPS).

The communication node 120 may include a communication node (e.g., userequipment (UE) or terminal) located on the ground and a communicationnode (e.g., airplane, drone) located on the non-ground. A service linkmay be established between the satellite 110 and the communication node120, and the service link may be a radio link. The satellite 110 mayprovide communication services to the communication node 120 using oneor more beams. A foot print of the beam of the satellite 110 may have anelliptical shape.

The communication node 120 may perform communications (e.g., downlinkcommunication, uplink communication) with the satellite 110 using theLTE technology and/or the NR technology. The communications between thesatellite 110 and the communication node 120 may be performed using anNR-Uu interface. When dual connectivity (DC) is supported, thecommunication node 120 may be connected to the satellite 110 as well asanother base station (e.g., base station supporting the LTE and/or NRfunctions), and the DC operation may be performed based on thetechnology defined in the LTE and/or NR technical specifications.

The gateway 130 may be located on the ground, and a feeder link may beestablished between the satellite 110 and the gateway 130. The feederlink may be a radio link. The gateway 130 may be referred to as a‘non-terrestrial network (NTN) gateway’. Communications between thesatellite 110 and the gateway 130 may be performed based on an NR-Uuinterface or a satellite radio interface (SRI). The gateway 130 may beconnected to the data network 140. A ‘core network’ may exist betweenthe gateway 130 and the data network 140. In this case, the gateway 130may be connected to the core network, and the core network may beconnected to the data network 140. The core network may support the NRtechnology. For example, the core network may include an access andmobility management function (AMF), a user plane function (UPF), asession management function (SMF), and the like. Communications betweenthe gateway 130 and the core network may be performed based on an NG-C/Uinterface.

Alternatively, a base station and the core network may exist between thegateway 130 and the data network 140. In this case, the gateway 130 maybe connected to the base station, the base station may be connected tothe core network, and the core network may be connected to the datanetwork 140. The base station and core network may support the NRtechnology. Communications between the gateway 130 and the base stationmay be performed based on an NR-Uu interface, and communications betweenthe base station and the core network (e.g., AMF, UPF, SMF) may beperformed based on an NG-C/U interface.

FIG. 2 is a conceptual diagram illustrating a second exemplaryembodiment of a non-terrestrial network.

As shown in FIG. 2 , a non-terrestrial network may include a satellite#1 211, a satellite #2 212, a communication node 220, a gateway 230, adata network 240, and the like. The non-terrestrial network shown inFIG. 2 may be a non-terrestrial network based on a regenerative payload.For example, each of the satellites #1 and #2 may perform a regenerativeoperation (e.g., demodulation operation, decoding operation, re-encodingoperation, re-modulation operation, and/or filtering operation) on apayload received from another entity (e.g., communication node 220 orgateway 230) constituting the non-terrestrial network, and transmit theregenerated payload.

Each of the satellites #1 and #2 may be an LEO satellite, a MEOsatellite, a GEO satellite, a HEO satellite, or a UAS platform. The UASplatform may include a HAPS. The satellite #1 211 may be connected tothe satellite #2 212, and an inter-satellite link (ISL) may beestablished between the satellite #1 211 and the satellite #2 212. TheISL may operate in a radio frequency (RF) frequency or an optical band.The ISL may be established optionally. The communication node 220 mayinclude a communication node (e.g., UE or terminal) located on theground and a communication node (e.g., airplane, drone) located on thenon-ground. A service link (e.g., radio link) may be established betweenthe satellite #1 211 and the communication node 220. The satellite #1211 may provide communication services to the communication node 220using one or more beams.

The communication node 220 may perform communications (e.g., downlinkcommunication, uplink communication) with the satellite #1 211 using theLTE technology and/or the NR technology. Communications between thesatellite #1 211 and the communication node 220 may be performed usingan NR-Uu interface. When DC is supported, the communication node 220 maybe connected with the satellite #1 211 as well as another base station(e.g., base station supporting the LTE and/or NR functions), and performthe DC operation based on the technology defined in the LTE and/or NRtechnical specifications.

The gateway 230 may be located on the ground, a feeder link may beestablished between the satellite #1 211 and the gateway 230, and afeeder link may be established between the satellite #2 212 and thegateway 230. The feeder link may be a radio link. When an ISL is notestablished between the satellite #1 211 and the satellite #2 212, thefeeder link between the satellite #1 211 and the gateway 230 may beestablished mandatorily.

Communications between each of the satellites #1 and #2 and the gateway230 may be performed based on an NR-Uu interface or SRI. The gateway 230may be connected to the data network 240. A ‘core network’ may existbetween the gateway 230 and the data network 240. In this case, thegateway 230 may be connected to the core network, and the core networkmay be connected to the data network 240. The core network may supportthe NR technology. For example, the core network may include AMF, UPF,SMF, and the like. Communications between the gateway 230 and the corenetwork may be performed based on an NG-C/U interface.

Alternatively, a base station and the core network may exist between thegateway 230 and the data network 240. In this case, the gateway 230 maybe connected to the base station, the base station may be connected tothe core network, and the core network may be connected to the datanetwork 240. The base station and core network may support the NRtechnology. Communications between the gateway 230 and the base stationmay be performed based on an NR-Uu interface, and communications betweenthe base station and the core network (e.g., AMF, UPF, SMF) may beperformed based on an NG-C/U interface.

Meanwhile, each of the entities (e.g., satellites, communication nodes,gateways, etc.) constituting the non-terrestrial network shown in FIGS.1 and 2 may be configured as follows.

FIG. 3 is a block diagram illustrating a first exemplary embodiment ofan entity constituting a non-terrestrial network.

As shown in FIG. 3 , an entity 300 may comprise at least one processor310, a memory 320, and a transceiver 330 connected to the network forperforming communications. In addition, the entity 300 may furthercomprise an input interface device 340, an output interface device 350,a storage device 360, and the like. Each component included in theentity 300 may communicate with each other as connected through a bus370.

However, each of the components included in the entity 300 may beconnected through a dedicated interface or bus based on the processor310 instead of the common bus 370. For example, the processor 310 may beconnected to at least one of the memory 320, the transceiver 330, theinput interface device 340, the output interface device 350, and thestorage device 360 through a dedicated interface.

The processor 310 may execute a program stored in at least one of thememory 320 and the storage device 360. The processor 310 may refer to acentral processing unit (CPU), a graphics processing unit (GPU), or adedicated processor on which methods in accordance with embodiments ofthe present disclosure are performed. Each of the memory 320 and thestorage device 360 may be constituted by at least one of a volatilestorage medium and a non-volatile storage medium. For example, thememory 320 may comprise at least one of read-only memory (ROM) andrandom access memory (RAM).

Meanwhile, scenarios in the non-terrestrial network may be defined asshown in Table 1 below.

TABLE 1 NTN shown in FIG. 1 NTN shown in FIG. 2 GEO Scenario A ScenarioB LEO Scenario C1 Scenario D1 (steerable beams) LEO Scenario C2 ScenarioD2 (beams moving with satellite)

The case when the satellite 110 is a GEO satellite (e.g., GEO satellitethat supports a transparent function) in the non-terrestrial networkshown in FIG. 1 may be referred to as ‘scenario A’. The case when thesatellites #1 and #2 are GEO satellites (e.g., GEO satellite supportingregenerative functions) in the non-terrestrial network shown in FIG. 2may be referred to as ‘scenario B’.

The case when the satellite 110 is an LEO satellite having steerablebeams in the non-terrestrial network shown in FIG. 1 may be referred toas ‘scenario C1’. The case when the satellite 110 is an LEO satellitehaving beams moving with the satellite in the non-terrestrial networkshown in FIG. 1 may be referred to as ‘scenario C2’. The case when thesatellites #1 and #2 are LEO satellites having steerable beams in thenon-terrestrial network shown in FIG. 2 may be referred to as ‘scenarioD1’. The case when the satellites #1 and #2 are LEO satellites havingbeams moving together with the satellite in the non-terrestrial networkshown in FIG. 2 may be referred to as ‘scenario D2’.

Parameters for the scenarios defined in Table 1 may be defined as shownin Table 2 below.

TABLE 2 Scenarios A and B Scenarios C and D Altitude 35,786 km   600 km1,200 km Spectrum (service <6 GHz (e g., 2 GHz) link) >6 GHz (e g., DL20 GHz, UL 30 GHz) Maximum channel 30 MHz for band < 6 GHz bandwidthcapability  1 GHz for band > 6 GHz (service link) Maximum distance40,581 km 1,932 km (600 km altitude) between a satellite 3,131 km (1,200km altitude) and a communication node (e.g., UE) at a minimum elevationangle Maximum round trip Scenario A: 541.46 ms Scenario C: (transparentdelay (RTD) (service and feeder links) payload: service and feeder(propagation delay Scenario B: 270.73 ms links) only) (service linkonly) 25.77 ms (600 km altitude) 41.77 ms (1200 km altitude) Scenario D:(regenerative payload: service link only) 12.89 ms (600 km altitude)20.89 ms (1200 km altitude) Maximum differential  10.3 m 3.12 ms (600 kmaltitude) delay within a cell 3.18 ms (1200 km altitude) Service link3GPP defined NR Feeder link 3GPP or non-3GPP defined radio interface

In addition, in the scenarios defined in Table 1, delay constraints maybe defined as shown in Table 3 below.

TABLE 3 Scenario A Scenario B Scenario C1-2 Scenario D1-2 Satellitealtitude 35,786 km 600 km Maximum RTD of a 541.75 ms 270.57 ms 28.41 ms12.88 ms radio interface (worst case) between a base station and a UEMinimum RTD of a 477.14 ms 238.57 ms 8 ms 4 ms radio interface between abase station and a UE

Hereinafter, retransmission methods based on statistical information ondecoding results of data will be described. Even when a method (e.g.,transmission or reception of a data packet) performed at a firstcommunication node among communication nodes is described, thecorresponding second communication node may perform a method (e.g.,reception or transmission of the data packet) corresponding to themethod performed at the first communication node. That is, when anoperation of a terminal is described, the corresponding base station mayperform an operation corresponding to the operation of the terminal.Conversely, when an operation of the base station is described, thecorresponding terminal may perform an operation corresponding to theoperation of the base station.

The retransmission method (e.g., retransmission mechanism) may bedesigned assuming a specific range of round trip time (RTT), and theretransmission method may depend on the RTT. Accordingly, when the RTTis changed, a new retransmission method may be required. Referring tothe scenarios described in Table 3, the RTT (e.g., RTD) in thenon-terrestrial network may be longer than the RTT in the conventionalcommunication network (e.g., LTE communication network, NR communicationnetwork). Therefore, for the non-terrestrial network, a newretransmission method that is tolerable to a delay may be requiredinstead of the retransmission method designed based on a relativelyshort RTT.

As a new retransmission method, a blind retransmission method (e.g.,multiple retransmission method) may be used. In the blind retransmissionmethod, data may be transmitted in slot(s) aggregated according to aslot aggregation scheme, and a HARQ response (e.g., acknowledgment (ACK)or negative ACK (NACK)) for the corresponding data may not betransmitted. That is, a feedback operation of the HARQ response may bedisabled. When the blind retransmission method is used, there may not bea HARQ response for the data. In this case, since the transmitting node(e.g., base station or terminal) may not know a state (e.g., throughput)of the link, resources for retransmission of the data may be wasted. Theabove-described slot aggregation scheme may be applied not only to thenon-terrestrial network, but also to other communication networks (e.g.,LTE communication system, NR communication system). In exemplaryembodiments, the transmitting node may be a communication node thattransmits data, and the receiving node may be a communication node thatreceives data. For example, when the transmitting node is a basestation, the receiving node may be a terminal. Alternatively, when thetransmitting node is a terminal, the receiving node may be a basestation or another terminal.

FIG. 4 is a conceptual diagram illustrating a first exemplary embodimentof a blind retransmission method in a communication system.

As shown in FIG. 4 , the blind retransmission method may be performedbased on the slot aggregation scheme, and the feedback operation of theHARQ response may not be performed. The transmitting node may repeatedlytransmit the same transport block (TB) (e.g., TB composed of the samedata unit) in aggregated slots (e.g., S slots). Here, S may be a naturalnumber. The number of aggregated slots may be indicated by a slotaggregation factor (SAF). The repetitive transmission operation of thesame TB may be performed in unit of the SAF (e.g., aggregatedtransmission period). In one aggregated transmission period, the same TBmay be transmitted more than once, and the same TB including differentinformation may be transmitted in each slot.

That is, transmitted information may be changed for each slot in oneaggregated transmission period. The transmitted information may berate-matched information selected from a circular buffer. Theinformation selected from the circular buffer may be determinedaccording to a redundancy version (RV). In the aggregated transmissionperiod, a value of an RV applied to a current TB may be determined basedon a value of an RV applied to an initial transmission TB and atransmission order of the current TB. The initial transmission TB may bea TB transmitted through the first slot in the aggregated transmissionperiod.

When the slot aggregation scheme is used, a HARQ response may begenerated based on a result of decoding data performed by the receivingnode (e.g., base station or terminal). In this case, the HARQ responsemay include a decoding result for each of all TBs received in theaggregated transmission period. As another example, instead of one TB,one HARQ response may be generated for all TBs received in theaggregated transmission period. That is, the HARQ response may begenerated on an aggregated transmission period basis. One HARQ responsemay be generated by bundling decoding results for all TBs received inone aggregated transmission period. For example, when cyclic redundancycheck (CRC) results for all TBs received in one aggregated transmissionperiod indicate CRC failures, the receiving node may transmit NACK tothe transmitting node as the HARQ response. When the CRC result(s) forone or more TB(s) received in one aggregated transmission periodindicate CRC OK, the receiving node may transmit ACK to the transmittingnode as the HARQ response.

FIG. 5 is a sequence chart illustrating a first exemplary embodiment ofa retransmission method in a communication system.

As shown in FIG. 5 , a communication system (e.g., LTE communicationsystem, NR communication system, non-terrestrial network) may include atransmitting node and a receiving node. The transmitting node may be acommunication node that transmits data, and the receiving node may be acommunication node that receives the data. Each of the transmitting nodeand the receiving node may be configured identically or similarly to thecommunication node 300 shown in FIG. 3 .

The transmitting node may configure transmission parameters (S501). Thetransmission parameters may include an effective code rate relatedparameter and/or a HARQ related parameter. The transmitting node maytransmit the transmission parameters to the receiving node (S502). Thetransmission parameters may be transmitted through one or a combinationof two or more of system information, radio resource control (RRC)message, medium access control (MAC) message, and physical (PHY)message. The system information may be a master information block (MIB)and/or system information block (SIB). The MAC message may be a messageincluding a MAC control element (CE). The PHY message may be controlinformation, and the control information may be downlink controlinformation (DCI), uplink control information (UCI), and/or sidelinkcontrol information (SCI).

The receiving node may receive the transmission parameters from thetransmitting node. The transmitting node may transmit a transport block(TB) to the receiving node based on the transmission parameters (S503).Here, the transmission operation may be performed on a TB basis. Thereceiving node may perform an operation of receiving the TB based on thetransmission parameters. For example, the receiving node may generate aHARQ response (e.g., ACK or NACK) based on a result of decoding the TB(S504). The receiving node may transmit the HARQ response to thetransmitting node (S505).

The transmitting node may receive the HARQ response from the receivingnode, and may identify whether the HARQ response is ACK or NACK (S506).When the HARQ response is ACK, the transmitting node may determine thatthe TB transmitted in the step S503 has been successfully received bythe receiving node, and may perform a transmission operation of a new TB(S507). Alternatively, if a new TB does not exist in the transmittingnode, the transmission operation of the TB may be terminated.

On the other hand, when the HARQ response is NACK, the transmitting nodemay reconfigure the transmission parameters by performing the step S501again, and may perform a retransmission operation of the TB based on thereconfigured transmission parameters. That is, the transmitting node mayperform a rate control operation on the retransmission TB based on theHARQ response (e.g., NACK). The transmission parameters for theretransmission TB may be set differently from the transmissionparameters for the initial transmission TB.

FIG. 6 is a sequence chart illustrating a second exemplary embodiment ofa retransmission method in a communication system.

As shown in FIG. 6 , a communication system (e.g., LTE communicationsystem, NR communication system, and non-terrestrial network) mayinclude a transmitting node and a receiving node. Each of thetransmitting node and the receiving node may be configured identicallyor similarly to the communication node 300 shown in FIG. 3 . Theretransmission method shown in FIG. 6 may be performed based on the slotaggregation scheme. For example, the same TB (e.g., TB composed of thesame data unit) may be repeatedly transmitted in an aggregatedtransmission period (e.g., slots indicated by the SAF). The TBsrepeatedly transmitted in one aggregated transmission period may havedifferent RVs.

The transmitting node may configure transmission parameters (S601). Thetransmission parameters may include an effective code rate relatedparameter and/or a HARQ related parameter. The transmitting node maytransmit the transmission parameters to the receiving node (S602). Thetransmission parameters may be transmitted through one or a combinationof two or more of system information, RRC message, MAC message, and PHYmessage. The receiving node may receive the transmission parameters fromthe transmitting node. The transmission parameters may be configured(e.g., updated) according to the number of transmissions or receptionsof the TB (S603). For example, the transmitting node may configure thetransmission parameters according to the number of transmissions of theTB in one aggregated transmission period, and the receiving node mayconfigure the transmission parameters according to the number ofreceptions of the TB in one aggregated transmission period.

The transmitting node may transmit the TB to the receiving node based onthe transmission parameters (S604). The transmitting node may repeatedlytransmit the TB by the number indicated by the SAF in the aggregatedtransmission period. For example, the transmitting node may compare thenumber of transmissions of the TB in the aggregated transmission periodand the SAF (S606-1). If the number of transmissions of the TB in theaggregated transmission period is less than the SAF, the transmittingnode may reconfigure the transmission parameters according to the numberof transmissions of the TB (S603), and transmit the TB to the receivingnode based on the reconfigured transmission parameters (S604).

On the other hand, if the number of transmissions of the TB in theaggregated transmission period is equal to the SAF, the transmittingnode may perform the steps after the step S606-1. For example, when aHARQ feedback operation is disabled, the transmitting node may perform atransmission operation of a new TB (S609). On the other hand, when theHARQ feedback operation is enabled, the transmitting node may receive aHARQ response from the receiving node and may operate based on thereceived HARQ response.

Meanwhile, the receiving node may perform an operation of receiving theTB based on the transmission parameters. For example, the receiving nodemay generate a HARQ response (e.g., ACK or NACK) based on a decodingresult of the TB (S605). The step S605 may be performed on a TB basis.The receiving node may compare the number of receptions of the TB in theaggregated transmission period and the SAF (S606-2). If the number ofreceptions of the TB in the aggregated transmission period is less thanthe SAF, the receiving node may reconfigure the transmission parametersaccording to the number of receptions of the TB (S603), and may performan operation of receiving the TB based on the reconfigured transmissionparameters. On the other hand, if the number of receptions of the TB inthe aggregated transmission period is equal to the SAF, the receivingnode may transmit a HARQ response for all TBs received in the aggregatedtransmission period to the transmitting node (S607). The step S607 maybe performed when the HARQ feedback operation is enabled. When the HARQfeedback operation is disabled, the receiving node may perform areception operation of a new TB without performing the step S607.

The HARQ response transmitted in the step S607 may include a decodingresult for each of all TBs received in the aggregated transmissionperiod. As another example, when the decoding results for all TBsreceived in the aggregated transmission period indicate failures, theHARQ response transmitted in the step S607 may be NACK. As anotherexample, when the decoding result for at least one TB received in theaggregated transmission period is successful, the HARQ responsetransmitted in the step S607 may be ACK.

The transmitting node may receive the HARQ response from the receivingnode, and may identify whether the HARQ response is ACK or NACK (S608).When the HARQ response is ACK, the transmitting node may determine thatthe TB transmitted in the step S604 has been successfully received bythe receiving node, and may perform a transmission operation of a new TBin the next aggregated transmission period (S609). On the other hand,when a new TB does not exist in the transmitting node, the transmissionoperation of the TB may be terminated.

On the other hand, when the HARQ response is NACK, the transmitting nodemay reconfigure the transmission parameters by performing the step S601again, and may perform a retransmission operation of the TB based on thereconfigured transmission parameters. That is, the transmitting node mayperform a rate control operation on the retransmission TB based on theHARQ response (e.g., NACK). The transmission parameters for theretransmission TB may be configured differently from the transmissionparameters for the initial transmission TB. The TB retransmissionoperation may be performed in a new aggregated transmission period.

Meanwhile, when the retransmission procedure is performed based on theslot aggregation scheme in the non-terrestrial network, the HARQresponse may not be fed back. That is, the step S607 may not beperformed in the exemplary embodiment shown in FIG. 6 . In this case, inorder to ensure reliability, the number of retransmissions of the TB maybe preconfigured. Since the HARQ response is not fed back, the HARQresponse may not be used to determine whether to retransmit the TB. Dueto this limitation, the number of retransmissions of the TB may bepreconfigured before transmission of the TB, and the TB may betransmitted by the preconfigured retransmission number. In the TBretransmission procedure, transmission parameters other than sometransmission parameters (e.g., RV) may be applied equally to the initialtransmission TB and the retransmission TB.

When there is no HARQ response, transmission parameters corresponding toa current state (e.g., channel state, reception state, etc.) may not bedetermined. For example, the transmission parameters may be configuredto satisfy a reliability higher than a reliability corresponding to thecurrent state, and in this case, resources may be wasted. Alternatively,the transmission parameters may be configured to satisfy a reliabilitylower than the reliability corresponding to the current state, and inthis case, the transmission may fail.

When the slot aggregation scheme is used, one HARQ response may begenerated by bundling a decoding result for each of all TBs received inone aggregated transmission period. The one HARQ response may be ACK orNACK for the entire aggregated transmission period, and may not indicateACK or NACK for each of the TBs received in one aggregated transmissionperiod. Therefore, the transmitting node may not be able to identify thenumber of ACKs generated in one aggregated transmission period based onthe one HARQ response. In this case, the transmitting node may notidentify whether the transmission parameters have an appropriatereliability corresponding to the current state, a lower reliability thanthe reliability corresponding to the current state, or a higherreliability than the reliability corresponding to the current state.

FIG. 7 is a conceptual diagram illustrating a first exemplary embodimentof a SAF required according to a result of decoding data in acommunication system.

As shown in FIG. 7 , an SAF may be one of transmission parameters. TheSAF may indicate S, and S may be a natural number. In a case 3, an SAFsmaller than the SAF corresponding to the current state may be used, andaccordingly, ACK may not occur in one aggregated transmission period.Meanwhile, in a case 2, an appropriate SAF corresponding to the currentstate may be used. In this case, one ACK may occur in one aggregatedtransmission period. Finally, in a case 1, an SAF larger than the SAFcorresponding to the current state may be used. In this case, two ormore decoding successes may occur in one aggregated transmission period.In this case, one HARQ response in one aggregated transmission periodmay be determined as ACK, and accordingly, the case 2 may not bedistinguished from the case 3 from the perspective of the transmitter.TB transmissions other than TB transmissions related to the firstdecoding success in one aggregated transmission period may beunnecessary. Resources (e.g., radio resources) may be wasted due tounnecessary TB transmissions. However, since the HARQ response for oneaggregated transmission period indicates a success of the entireaggregated transmission period as one HARQ response and does notindicate the resources wasted by the current transmission, it is noteasy to reduce the wasted resources.

Meanwhile, in exemplary embodiments, the transmission parameters mayinclude an effective code rate related parameter and/or a HARQ relatedparameter (e.g., retransmission-related parameters). The effective coderate related parameter may include one or more parameters defined inTable 4 below, and the HARQ related parameter may include one or moreparameters defined in Table 5 below.

TABLE 4 Effective code rate related parameters Aggregation factor Numberof transmissions Number of layers TB size Resource mapping Number of RBs(e.g., Mapping type information (e.g., number of subcarriers) Bitmapnumber of REs) Bandwidth part (BWP) start, BWP size Resource indicationvalue (RIV) Number of symbols (e.g., start and length indicator value(SLIV)) MCS index Target code rate Modulation order Spectrum efficiencyNumber of overheads

TABLE 5 HARQ related parameters HARQ process ID Number of HARQ processesHARQ process number Redundancy version (RV) New data indicator (NDI)Code block group transmission information (CBGTI) Code block groupflushing out information (CBGFI)

In order to solve the above problem, retransmission methods may beperformed as follows.

1) Uplink Transmission Procedure

In the uplink transmission procedure, the decoding result and the HARQresponse may be generated by the base station (e.g., reception unitincluded in the base station), and the transmission parameters may beconfigured by the base station. Therefore, even when the HARQ operation(e.g., feedback operation of the HARQ response) is disabled in theuplink transmission procedure, the base station may generate the HARQresponse (e.g., ACK or NACK) based on a decoding result for uplink datareceived from the terminal, and configure the transmission parameters byusing the decoding result.

When the transmission parameters are changed, the base station mayinform the terminal of the changed transmission parameters. For example,the base station may transmit the changed transmission parameters to theterminal through one or a combination of two or more of systeminformation, RRC message, MAC message, and PHY message. In order toquickly transmit the transmission parameters, a MAC message and/or PHYmessage may be used. In this case, specific transmission parameters(e.g., SAF) may be transmitted through a MAC message and/or PHY message.

2) Downlink Transmission Procedure

In the downlink transmission procedure, the decoding result and the HARQresponse may be generated by the terminal (e.g., reception unit includedin the terminal), and the transmission parameters may be configured bythe base station. When the HARQ response is not transmitted to the basestation, the HARQ response may not be used to determine the transmissionparameters.

2-1) Method of Substituting the HARQ Response

When channel reciprocity is established, downlink performance (e.g.,downlink channel state) may be estimated based on uplink performance(e.g., uplink channel state). Accordingly, the base station may estimatea HARQ response for downlink data (hereinafter, referred to as ‘downlinkHARQ response’) based on a HARQ response for uplink data (hereinafter,referred to as ‘uplink HARQ response’). In this case, the base stationmay simply determine that the downlink HARQ response is the same as theuplink HARQ response. Alternatively, when an uplink metric is similar toa downlink metric, the base station may regard the uplink HARQ responseas the downlink HARQ response.

When the uplink metric is not similar to the downlink metric, the basestation may predict the downlink HARQ response using the uplink HARQresponse. Here, the metric may be one or more of an effective code rate,spectrum efficiency, and channel stat information (CSI) feedbackinformation. Information other than the above-described information maybe used as the metric. Also, the above procedure may be applied bysubstituting the HARQ response with a decoding result.

2-2) Method of Generating Statistical Information by StatisticallyCollecting Decoding Results, and Feeding Back Statistical Information

The terminal may receive one or more TBs from the base station, maygenerate a decoding result for each of the one or more TBs, and maygenerate statistical information on the decoding results. Thestatistical information may include at least one of a probability momentvalue such as an average and a deviation, minimum value, maximum value,average value, and difference for M transmissions and/or a time durationN. The probability moment value used as the statistical information maybe preconfigured. When M or more samples (e.g., TBs) are received, thestatistical information may be generated. Alternatively, when samplescorresponding to the time duration N are obtained, the statisticalinformation may be generated.

For example, the base station may determine a value used as thestatistical information, and inform the terminal of the determined valueusing one or a combination of two or more of system information, RRCmessage, MAC message, and PHY message. Alternatively, the terminal maydetermine a value used as the statistical information, and inform thebase station of the determined value using one or a combination of twoor more of RRC message, MAC message, and PHY message.

M and N may be preconfigured. M may be a natural number. N may be arational number, and a time unit may be microsecond (μs), millisecond(ms), or second (s). For example, the base station may determine Mand/or N, and may inform the terminal of M and/or N using one or acombination of two or more of system information, RRC message, MACmessage, and PHY message. Alternatively, the terminal may determine Mand/or N, and may inform the base station of M and/or N by using one ora combination of two or more of RRC message, MAC message, and PHYmessage.

The statistical information on the decoding results may include one ormore information elements defined in Table 6 below. The informationelement(s) used as the statistical information may be preconfigured. Forexample, the base station may determine the information element(s) usedas the statistical information, and inform the terminal of thedetermined information element(s) by using one or a combination of twoor more of system information, RRC message, MAC message, and PHYmessage. Alternatively, the terminal may determine the informationelement(s) used as the statistical information, and inform the basestation of the determined information element(s) by using one or acombination of two or more of RRC message, MAC message, and PHY message.

TABLE 6 Statistical information Statistical information indicating theposition in which the first decoding success occurring in one or moreaggregated transmission periods (e.g., an average of indexes of slotswhere the first CRC OK occurs, an average of positions associated of TBswith the first CRC OK) Statistical information indicating the number ofdecoding successes occurring in one or more aggregated transmissionperiods (e.g., average number) Statistical information indicating thenumber of decoding failures occurring in one or more aggregatedtransmission periods (e.g., average number) Statistical informationindicating the ratio of decoding success (or decoding failure) occurringin one or more aggregated transmission periods (e.g., average decodingsuccess rate or average decoding failure rate) Information indicatingthat the effective code rate is too low (e.g., information indicatingwhether the average number of decoding successes occurring in one ormore aggregated transmission periods exceeds 1 (or exceeds 1.5 or 2))Information indicating that the effective code rate is too high (e.g.,information indicating whether the average number of decoding failuresoccurring in one or more aggregated transmission periods exceeds (SAF-1)(or exceeds (SAF-0.5) or is equal to the SAF)) Information indicatingthe number of aggregated transmission periods Information indicating thenumber of TBs Transmission parameters (e.g., effective code rate ratedparameter and/or HARQ related parameter)

(1) Statistical Information Feedback Method

The terminal may generate the statistical information including one ormore information elements defined in Table 6, and may transmit thestatistical information to the base station through one or a combinationof two or more of RRC message, MAC message, and PHY message. Theinformation element(s) included in the statistical information may bepreconfigured by the base station or the terminal. The statisticalinformation may be transmitted from the terminal to the base station ata preconfigured transmission time. The transmission time of thestatistical information may be preconfigured. For example, the basestation may determine the transmission time of the statisticalinformation, and inform the terminal of the determined transmission timethrough one or a combination of two or more of system information, RRCmessage, MAC message, and PHY message.

Alternatively, the terminal may determine the transmission time of thestatistical information, and may inform the base station of thedetermined transmission time through one or a combination of two or moreof system information, RRC message, MAC message, and PHY message. Inthis case, the base station may reconfigure the transmission parametersin consideration of the transmission time configured by the terminal.

The terminal may transmit information elements required for configuringthe transmission parameters to the base station. In this case, the basestation may determine whether to apply the information elements receivedfrom the terminal. When it is necessary to apply the informationelements received from the terminal, the base station may determine theefficiency of the transmission parameters, and may change thetransmission parameters according to a result of the determination ofthe efficiency.

(2) Feedback Method of Information Indicating Whether TransmissionParameters are Efficient

The terminal may generate the statistical information on the decodingresults. Thereafter, the terminal may determine efficiency of thetransmission parameters, and transmit information indicating whether thetransmission parameters are efficient (hereinafter referred to as‘efficiency information’) to the base station through one or acombination of one or more of RRC message, MAC message, and PHY message.The base station may receive the efficiency information from theterminal, and may reconfigure the transmission parameters inconsideration of the efficiency information.

For example, the metric used to determine the efficiency of thetransmission parameters may be the statistical information (e.g.,average number) of the number of decoding successes occurring in one ormore aggregated transmission periods. In this case, if the averagenumber of decoding successes occurring in the aggregated transmissionperiod exceeds 1, the terminal may determine that the transmissionparameters need to be changed. That is, the terminal may determine thatthe transmission parameters are not efficient and may transmitefficiency information indicating that the transmission parameters arenot efficient to the base station. Here, it may be necessary to changein a direction in which the effective code rate increases. For example,it may be necessary to change in a direction in which the aggregationfactor decreases among the effective code rate related parameters, andthe corresponding information may be indicated by the efficiencyinformation. Here, conditions for determining that the transmissionparameters need to be changed may be variously changed. For example, theconditions may include ‘whether the average number of decoding successesexceeds 1.5’, ‘whether the average number of decoding successes exceeds2 or more’, and/or the like.

When the average number of decoding successes occurring in theaggregated transmission period is 1, the terminal may determine that thetransmission parameters are efficient and may transmit efficiencyinformation indicating that the transmission parameters are efficient tothe base station. Alternatively, since there is no need to change thetransmission parameters, the terminal may not perform an additionaloperation. Here, the conditions for determining that the transmissionparameters need to be changed may be variously changed. For example, theconditions may include ‘whether the average number of decoding successesis between 0.5 and 1.5’, and/or the like.

When the average number of decoding successes in the aggregatedtransmission period is less than 1, the terminal may determine that thetransmission parameters need to be changed. That is, the terminal maydetermine that the transmission parameters are not efficient and maytransmit efficiency information indicating that the transmissionparameters are not efficient to the base station. Here, it may benecessary to change the transmission parameters in a direction in whichthe effective code rate decreases. For example, it may be necessary tochange in a direction in which the aggregation factor increases amongeffective code rate related parameters, and the correspondinginformation may be indicated by the efficiency information. Here, theconditions for determining that the transmission parameters need to bechanged may be variously changed. For example, the conditions mayinclude ‘whether the average number of decoding successes is less than0.5’, ‘whether no decoding success occurs’, and/or the like.

The above-described exemplary embodiment may be performed for not onlythe aggregation factor but also other parameters. In this case, anexecution order or priority may be preconfigured. For example, the basestation may determine the execution order or priority of the efficiencyinformation generation/transmission operation, and inform the terminalof the determined execution order or the determined priority through oneor a combination of one or more of system information, RRC message, MACmessage, and PHY message. Alternatively, the terminal may determine theexecution order or priority of the efficiency informationgeneration/transmission operation, and inform the base station of thedetermined execution order or the determined priority through one or acombination of two or more of RRC message, MAC message, and PHY message.

Meanwhile, the transmission time of the efficiency information may bepreconfigured. For example, the base station may determine thetransmission time of the efficiency information, and may inform theterminal of the determined transmission timing through one or acombination of two or more of system information, RRC message, MACmessage, and PHY message. Alternatively, the terminal may determine thetransmission time of the efficiency information, and may inform the basestation of the determined transmission time through one or a combinationof two or more of RRC message, MAC message, and PHY message.

In the efficiency information feedback procedure, one or more ofinformation indicating that the transmission parameters need to bechanged, changed transmission parameters (e.g., changed effective coderate), transmission parameters required to be changed, and a differencebetween the current transmission parameter and a target transmissionparameter (e.g., a difference between the current effective code rateand a target effective code rate) may be fed back together with theefficiency information. Alternatively, information indicating up, down,or maintenance of the transmission parameter may be transmitted.

The terminal may transmit the information indicating whether it isnecessary to change the transmission parameters to the base station. Thebase station may determine whether to apply the information receivedfrom the terminal, and may change the transmission parameters whenapplication of the information is required.

A comparison criterion (e.g., metric) used to determine the efficiencyof the transmission parameters may be a target error rate, throughput,latency, and/or transmission parameter. A value of the metric used todetermine the efficiency of the transmission parameter may be calculatedbased on a quality of service (QoS) condition. The value of the metricused to determine the efficiency of the transmission parameter may beindicated by a higher layer. The value of the metric used to determinethe efficiency of the transmission parameter may be preconfigured. Forexample, the base station may determine the value of the metric used todetermine the efficiency of the transmission parameter, and inform thedetermined value to the terminal through a combination of one or more ofsystem information, RRC message, MAC message, and PHY message.Alternatively, the terminal may determine the value of the metric usedto determine the efficiency of the transmission parameter, and mayinform the base station of the determined value through one or acombination of two or more of RRC message, MAC message, and PHY message.

(3) Feedback Method of Guide Information for Changing TransmissionParameters

The terminal may generate the statistical information on the decodingresults and may transmit the efficiency information to the base station.In addition, the terminal may reconfigure the transmission parameters,and transmit the reconfigured transmission parameters (or guideinformation on the reconfigured transmission parameters) to the basestation through one or a combination of two or more of RRC message, MACmessage, and PHY message. The transmission time of the reconfiguredtransmission parameters (or guide information on the reconfiguredtransmission parameters) may be preconfigured. The base station maydetermine the transmission time of the reconfigured transmissionparameters (or guide information on the reconfigured transmissionparameters), and may inform the terminal of the determined transmissiontime through one or a combination of two or more of system information,RRC message, MAC message, and PHY message. Alternatively, the terminalmay determine the transmission time of the reconfigured transmissionparameters (or guide information on the reconfigured transmissionparameters), and may inform the base station of the determinedtransmission time through one or a combination of two or more of RRCmessage, MAC message, and PHY message.

The guide information for changing the transmission parameters may beused as a guideline for determining a transmission parameter to bechanged and/or a value of the transmission parameter to be changed. Atransmission parameter transmitted as the guide information for changingthe transmission parameter may be preconfigured. The base station maydetermine a transmission parameter used as the guide information forchanging the transmission parameter, and may inform the terminal of thedetermined transmission parameter through one or a combination of two ormore of system information, RRC message, MAC message, and PHY message.Alternatively, the terminal may determine a transmission parameter usedas guide information for changing the transmission parameter, and mayinform the base station of the determined transmission parameter throughone or a combination of two or more of RRC message, MAC message, and PHYmessage.

In the guide information feedback procedure, at least one of theinformation indicating that the transmission parameters need to bechanged, the changed transmission parameters, the transmissionparameters required to be changed, and a difference between the currenttransmission parameter and the target transmission parameter may be fedback together with the guide information. Alternatively, informationindicating up, down, or maintenance of the transmission parameter may betransmitted.

The terminal may transmit the guide information for changing thetransmission parameters to the base station. The base station maydetermine whether to apply the guide information received from theterminal, and may change the transmission parameters based on the guideinformation when it is necessary to apply the guide information.

For example, the metric used to determine whether the guide informationof the transmission parameter is fed back may be the statisticalinformation on the number (e.g., average number) of decoding successesoccurring one or more aggregated transmission periods. In this case, ifthe average number of decoding successes in the aggregated transmissionperiod exceeds 1, the terminal may determine that the transmissionparameters need to be changed, and transmit the guide information of thetransmission parameters to the base station. Here, the guide informationmay suggest an increase in the effective code rate. For example, theguide information may suggest a decrease of the aggregation factor amongparameters related to the effective code rate. However, when theaggregation factor is already set to the minimum value, the guideinformation may suggest changing another parameter among the effectivecode rate related parameters. Here, conditions for determining that thetransmission parameter needs to be changed may be variously changed. Forexample, the conditions may include ‘whether the average number ofdecoding successes exceeds 1.5’, ‘ whether the average number ofdecoding successes is equal to or greater than 2’, and/or the like.

If the average number of decoding successes occurring in the aggregatedtransmission period is 1, the terminal may determine that it is notnecessary to change the transmission parameters, and may not transmitthe guide information to the base station. That is, the terminal may notperform an additional operation. Here, the conditions for determiningthat the transmission parameters need to be changed may be variouslychanged. For example, the conditions may include ‘whether the averagenumber of decoding successes is between 0.5 and 1.5’, and/or the like.

If the average number of decoding successes in the aggregatedtransmission period is less than 1, the terminal may determine that thetransmission parameter needs to be changed and transmit guideinformation of the transmission parameter to the base station. Here, theguide information may suggest a decrease in the effective code rate. Forexample, the guide information may suggest an increase in theaggregation factor among the effective code rate related parameters.However, when the aggregation factor is already set to the maximumvalue, the guide information may suggest changing other parameters amongthe effective code rate related parameters. Here, the conditions fordetermining whether the transmission parameters need to be changed maybe variously changed. For example, the conditions may include ‘whetherthe average number of decoding successes is less than 0.5’, ‘whether nodecoding success occurs’, and/or the like.

The above-described exemplary embodiment may be performed for not onlythe aggregation factor but also other parameters. In this case, anexecution order or priority may be preconfigured. For example, the basestation may determine the execution order or priority of the guideinformation generation/transmission operation, and inform the terminalof the determined execution order or the determined priority through oneor a combination of one or more of system information, RRC message, MACmessage, and PHY message. Alternatively, the terminal may determine theexecution order or priority of the guide informationgeneration/transmission operation, and inform the base station of thedetermined execution order or the determined priority through one or acombination of two or more of RRC message, MAC message, and PHY message.

FIG. 8 is a sequence chart illustrating a third exemplary embodiment ofa retransmission method in a communication system.

As shown in FIG. 8 , a communication system (e.g., LTE communicationsystem, NR communication system, and non-terrestrial network) mayinclude a transmitting node and a receiving node. Each of thetransmitting node and the receiving node may be configured identicallyor similarly to the communication node 300 shown in FIG. 3 . Theretransmission method shown in FIG. 8 may be performed based on the slotaggregation scheme. For example, the same TB may be repeatedlytransmitted in an aggregated transmission period (e.g., slots indicatedby the SAF). The TBs repeatedly transmitted in one aggregatedtransmission period may have different RVs.

The transmitting node may configure transmission parameters (S801). Thetransmission parameters may include an effective code rate relatedparameter and/or a HARQ related parameter. The transmitting node maytransmit the transmission parameters to the receiving node (S802). Thetransmission parameters may be transmitted through one or a combinationof two or more of system information, RRC message, MAC message, and PHYmessage. The receiving node may receive the transmission parameters fromthe transmitting node. The transmission parameters may be configured(e.g., updated) according to the number of transmissions or receptionsof the TB (S803). For example, the transmitting node may configure thetransmission parameters according to the number of transmissions of theTB in one aggregated transmission period, and the receiving node mayconfigure the transmission parameters according to the number ofreceptions of the TB in one aggregated transmission period.

The transmitting node may transmit the TB to the receiving node based onthe transmission parameters (S804). The transmitting node may repeatedlytransmit the TB by the number indicated by the SAF in the aggregatedtransmission period. For example, the transmitting node may compare thenumber of transmissions of the TB and the SAF in the aggregatedtransmission period (S809-1). If the number of TB transmissions in theaggregated transmission period is less than the SAF, the transmittingnode may reconfigure the transmission parameters according to the numberof transmissions of the TB (S803), and transmit the TB to the receivingnode based on the reconfigured transmission parameters (S804). On theother hand, if the number of transmissions of the TB in the aggregatedtransmission period is the same as the SAF, the transmitting node mayterminate the transmission operation in the aggregated transmissionperiod, and may perform a transmission operation (e.g., transmissionoperation for a new TB) in a new aggregated transmission period (S810).In the new aggregated transmission period, the transmission operationmay be performed based on the steps S801, S802, S803, S804, and S809-1.

Meanwhile, the receiving node may perform a TB receiving operation basedon the transmission parameters. For example, the receiving node maygenerate a decoding result of the TB (S805). The step S805 may beperformed on a TB or slot basis. The receiving node may generatestatistical information, efficiency information, and/or guideinformation on the decoding result (S806). The statistical information,efficiency information, and/or guide information may be generated basedon the above-described scheme. The receiving node may determine whethera feedback condition of the information generated in the step S806(e.g., statistical information, efficiency information, and/or guideinformation) is satisfied (S807).

For example, the feedback condition may be a transmission time. In thiscase, the receiving node may determine that the feedback condition issatisfied when a preconfigured transmission time is reached, and maytransmit the statistical information, efficiency information, and/orguide information to the transmitting node at the preconfiguredtransmission time (S808). The information generated in the step S806 maybe transmitted through one or a combination of two or more of RRCmessage, MAC message, and PHY message. As another example, the feedbackcondition may be a necessity of reconfiguring the transmissionparameters. In this case, the receiving node may determine that it isnecessary to reconfigure the transmission parameters based on thedecoding result generated in the step S805 and/or the informationgenerated in the step S806, and in this case, the statisticalinformation, efficiency information, and/or guide information may betransmitted to the transmitting node (S808).

If the feedback condition is not satisfied, the statistical information,efficiency information, and/or guide information may not be transmitted.For example, when the feedback condition is not satisfied in oneaggregated transmission period, the statistical information, efficiencyinformation, and/or guide information may not be transmitted before theend of the one aggregated transmission period. Alternatively, thestatistical information, efficiency information, and/or guideinformation may be transmitted regardless of the feedback condition. Ifthe steps S806 to S808 are performed after the step S805, the entirecommunication procedure may be performed without a problem. Theexecution timing of the steps S806 to S808 may not be limited to theexemplary embodiment shown in FIG. 8 .

The transmitting node may receive the statistical information,efficiency information, and/or guide information from the receivingnode, and may reconfigure the transmission parameters in considerationof the statistical information, efficiency information, and/or guideinformation. The reconfigured transmission parameters may be transmittedto the receiving node. When the statistical information, efficiencyinformation, and/or guide information are received from the receivingnode before the end of the aggregated transmission period #n, thetransmitting node may not apply the statistical information, efficiencyinformation, and/or guide information to the transmission operation forthe aggregated transmission period #n.

That is, the transmitting node may apply the statistical information,efficiency information, and/or guide information received in theaggregated transmission period #n to a transmission form a newaggregated transmission period (e.g., aggregated transmission period#n+k) after the aggregated transmission period #n. The transmissionparameters for the aggregated transmission period #n+k may be configuredin consideration of the statistical information, efficiency information,and/or guide information received in the aggregated transmission period#n. Here, each of n and k may be a natural number. Alternatively, thetransmitting node may reconfigure the transmission parameters for theaggregated transmission period #n in consideration of the statisticalinformation, efficiency information, and/or guide information receivedin the aggregated transmission period #n, and use the reconfiguredtransmission parameters to perform the transmission operation in theaggregated transmission period #n. The reconfigured transmissionparameters may be transmitted to the receiving node.

Meanwhile, after performing the step S807 or S808, the receiving nodemay compare the number of receptions of the TB in the aggregatedtransmission period and the SAF (S809-2). If the number of receptions ofthe TB in the aggregated transmission period is less than the SAF, thereceiving node may reconfigure the transmission parameters according tothe number of receptions of the TB (S803), and may perform an operationof receiving the TB based on the reconfigured transmission parameters.On the other hand, if the number of transmissions of the TB in theaggregated transmission period is equal to the SAF, the receiving nodemay terminate the reception operation in the aggregated transmissionperiod, and may perform a reception operation in a new aggregatedtransmission period (e.g., reception operation of a new TB (S810). Inthe new aggregated transmission period, the reception operation may beperformed based on the steps S802 to S809-2.

FIG. 9 is a sequence chart illustrating a fourth exemplary embodiment ofa retransmission method in a communication system.

As shown in FIG. 9 , a communication system (e.g., LTE communicationsystem, NR communication system, and non-terrestrial network) mayinclude a transmitting node and a receiving node. Each of thetransmitting node and the receiving node may be configured identicallyor similarly to the communication node 300 shown in FIG. 3 . Theretransmission method shown in FIG. 9 may be performed based on the slotaggregation scheme. For example, the same TB may be repeatedlytransmitted in an aggregated transmission period (e.g., slots indicatedby the SAF). The TBs repeatedly transmitted in one aggregatedtransmission period may have different RVs.

Steps S901 to S909-2 shown in FIG. 9 may be performed in the same manneras the steps S801 to S809-2 shown in FIG. 8 . The exemplary embodimentshown in FIG. 9 may further include ‘an operation of transmitting andreceiving a HARQ response for all TBs received in an aggregatedtransmission period’ compared to the exemplary embodiment shown in FIG.8 .

For example, the receiving node may compare the number of receptions ofthe TB in the aggregated transmission period and the SAF. When thenumber of receptions of TBs in the aggregated transmission period isequal to the SAF, the receiving node may transmit the HARQ response forall TBs received in the aggregated reception period to the transmittingnode (S910).

The HARQ response transmitted in the step S910 may include a decodingresult for each of all TBs received in the aggregated transmissionperiod. As another example, when the decoding results for all TBsreceived in the aggregated transmission period indicate CRC failure, theHARQ response transmitted in the step S910 may be NACK. As anotherexample, when the decoding result for at least one TB received in theaggregated transmission period indicates CRC OK, the HARQ responsetransmitted in the step S910 may be ACK.

The transmitting node may receive the HARQ response from the receivingnode, and may identify whether the HARQ response is ACK or NACK (S911).If the HARQ response is ACK, the transmitting node may determine thatthe TB transmitted in the step S904 has been successfully received bythe receiving node, and may perform a new TB transmission operation inthe next aggregated transmission period (S912). Alternatively, if a newTB does not exist in the transmitting node, the transmission operationof the TB may be terminated. On the other hand, when the HARQ responseis NACK, the transmitting node may reconfigure the transmissionparameters by performing the step S901 again, and may perform aretransmission operation of the TB based on the reconfiguredtransmission parameters. The receiving node that has transmitted the ACKin the step S910 may perform a new TB reception operation in the nextaggregated transmission period (S912).

Meanwhile, if the steps S906 to S908 are performed after the step S905,the entire communication procedure may be performed without a problem.The execution timing of the steps S906 to S908 may not be limited to theexemplary embodiment shown in FIG. 9 .

FIG. 10 is a sequence chart showing a fifth exemplary embodiment of aretransmission method in a communication system.

As shown in FIG. 10 , a communication system (e.g., LTE communicationsystem, NR communication system, and non-terrestrial network) mayinclude a transmitting node and a receiving node. Each of thetransmitting node and the receiving node may be configured identicallyor similarly to the communication node 300 shown in FIG. 3 .

The retransmission method shown in FIG. 10 may be a generalretransmission method rather than the blind retransmission method. Thatis, in the exemplary embodiment shown in FIG. 10 , the slot aggregationscheme may not be used. Steps S1001 to S1004 shown in FIG. 10 may beperformed in the same manner as the steps S501 to S504 shown in FIG. 5 .The exemplary embodiment shown in FIG. 10 may further include stepsS1005 to S1007 compared to the exemplary embodiment shown in FIG. 5 .The steps S1005 to S1007 shown in FIG. 10 may be performed in the samemanner as the steps S806 to S808 shown in FIG. 8 .

Meanwhile, after performing the step S1006 or step S1007, the receivingnode may transmit a HARQ response (e.g., ACK or NACK) for the TB to thetransmitting node (S1008). In the exemplary embodiment shown in FIG. 10, since the HARQ response for the TB is transmitted, the steps S1005 toS1007 may be omitted. In this case, the step S1008 may be performedafter the step S1004.

The transmitting node may receive the HARQ response from the receivingnode, and may identify whether the HARQ response is ACK or NACK (S1009).If the HARQ response is ACK, the transmitting node may determine thatthe TB transmitted in the step S1003 has been successfully received bythe receiving node, and may perform a transmission operation of a new TB(S1010). The transmission parameters for the new TB may be configured inconsideration of statistical information, efficiency information, and/orguide information received from the receiving node. Alternatively, if anew TB does not exist in the transmitting node, the transmissionoperation of the TB may be terminated.

On the other hand, if the HARQ response is NACK, the transmitting nodemay reconfigure the transmission parameters by performing the step S1001again, and may perform a retransmission operation of the TB based on thereconfigured transmission parameters. Here, the transmission parametersfor retransmission of TB may be reconfigured in consideration ofstatistical information, efficiency information, and/or guideinformation received from the receiving node.

Meanwhile, if the steps S1005 to S1007 are performed after the stepS1004, the entire communication procedure may be performed without aproblem. The execution timing of the steps S1005 to S1007 may not belimited to the exemplary embodiment shown in FIG. 10 . For example, ifthe steps S1005 to S1007 are performed only before the end of the TB,the entire communication procedure may be performed without a problem.

Meanwhile, in the above-described retransmission methods (e.g., theretransmission methods shown in FIGS. 5, 6, 8, 9 , and/or 10), theinformation indicating enabling or disabling of the HARQ feedbackoperation may be configured as a separate transmission parameter. Inthis case, the retransmission method may be performed according to anenabled or disabled state of the HARQ feedback operation.

The HARQ feedback operation may be partially enabled or disabled by aspecific granularity (e.g., a logical channel identifier (LCD), HARQprocess). In this case, separate transmission parameters may beconfigured for each of the granularity, granularity subset, orgranularity group, and the retransmission method may be managed. Whenthe HARQ feedback operation is partially enabled or disabled, the HARQresponse according to the enabled HARQ feedback operation may be appliedto the disabled HARQ feedback operation.

The exemplary embodiments of the present disclosure may be implementedas program instructions executable by a variety of computers andrecorded on a computer readable medium. The computer readable medium mayinclude a program instruction, a data file, a data structure, or acombination thereof. The program instructions recorded on the computerreadable medium may be designed and configured specifically for thepresent disclosure or can be publicly known and available to those whoare skilled in the field of computer software.

Examples of the computer readable medium may include a hardware devicesuch as ROM, RAM, and flash memory, which are specifically configured tostore and execute the program instructions. Examples of the programinstructions include machine codes made by, for example, a compiler, aswell as high-level language codes executable by a computer, using aninterpreter. The above exemplary hardware device can be configured tooperate as at least one software module in order to perform theembodiments of the present disclosure, and vice versa.

While the embodiments of the present disclosure and their advantageshave been described in detail, it should be understood that variouschanges, substitutions and alterations may be made herein withoutdeparting from the scope of the present disclosure.

What is claimed is:
 1. An operation method of a first communication nodein a communication system, the operation method comprising: receivingtransmission parameters from a second communication node; transmitting aplurality of transport blocks (TBs) including a same data unit #1 to thesecond communication node based on the transmission parameters in anaggregated transmission period #n including a plurality of slots; andreceiving changed transmission parameters which are generated inconsideration of statistical information from the second communicationnode, wherein the statistical information are decoding results in theaggregated transmission period #n, the statistical information of theaggregated transmission period #n is used for determining an effectivecode rate applied to an aggregated transmission period #n+k includingone or more slots after the aggregated transmission period #n, one ormore TBs including a same data unit #2 are transmitted in the aggregatedtransmission period #n+k, each of the aggregated transmission periods #nand #n+k is used for repeated transmission of a TB including a same dataunit, and each of n and k is a natural number.
 2. The operation methodaccording to claim 1, further comprising transmitting the one or moreTBs to the second communication node based on the changed transmissionparameters in the aggregated transmission period #n+k.
 3. The operationmethod according to claim 1, wherein the statistical informationincludes at least one of information indicating a number of decodingsuccesses occurring in a plurality of aggregated transmission periods,information indicating a number of decoding failures occurring in theplurality of aggregated transmission periods, or information indicatinga position of a first decoding success occurring in the plurality ofaggregated transmission periods.
 4. The operation method according toclaim 1, wherein the statistical information includes at least one ofinformation indicating a number of decoding successes occurring in theaggregated transmission period #n, information indicating a number ofdecoding failures occurring in the aggregated transmission period #n, orinformation indicating a position of a first decoding success occurringin the aggregated transmission period #n.
 5. The operation methodaccording to claim 1, wherein the same data unit #2 is different fromthe same data unit #1 which is transmitted in the aggregatedtransmission period #n.
 6. A first communication node in a communicationsystem, the first communication node comprising: a processor, whereinthe processor causes the first communication node to: receivetransmission parameters from a second communication node; transmit aplurality of transport blocks (TBs) including a same data unit #1 to thesecond communication node based on the transmission parameters in anaggregated transmission period #n including a plurality of slots; andreceive changed transmission parameters which are generated inconsideration of statistical information from the second communicationnode, wherein the statistical information are decoding results in theaggregated transmission period #n, the statistical information of theaggregated transmission period #n is used for determining an effectivecode rate applied to an aggregated transmission period #n+k includingone or more slots after the aggregated transmission period #n, one ormore TBs including a same data unit #2 are transmitted in the aggregatedtransmission period #n+k, each of the aggregated transmission periods #nand #n+k is used for repeated transmission of a TB including a same dataunit, and each of n and k is a natural number.
 7. The firstcommunication node according to claim 6, further comprising transmittingthe one or more TBs to the second communication node based on thechanged transmission parameters in the aggregated transmission period#n+k.
 8. The first communication node according to claim 6, wherein thestatistical information includes at least one of information indicatinga number of decoding successes occurring in a plurality of aggregatedtransmission periods, information indicating a number of decodingfailures occurring in the plurality of aggregated transmission periods,or information indicating a position of a first decoding successoccurring in the plurality of aggregated transmission periods.
 9. Thefirst communication node according to claim 6, wherein the statisticalinformation includes at least one of information indicating a number ofdecoding successes occurring in the aggregated transmission period #n,information indicating a number of decoding failures occurring in theaggregated transmission period #n, or information indicating a positionof a first decoding success occurring in the aggregated transmissionperiod #n.
 10. The first communication node according to claim 6,wherein the same data unit #2 is different from the same data unit #1which is transmitted in the aggregated transmission period #n.